Rotary drier



B. M. HESS ROTARY DRIER Feb. 5, 1957 3 Sheets-Sheet l Filed Oct. 8, 1953 a A ,Nw

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B. M. HESS ROTARY DRIER Feb. 5, 1.957

3 Sheets-Sheet 2 Filed 001'.. 8, 1955 Feb. 5, 195'?M B. M, Hl-:ss 2,780,010

ROTARY DRIER v Filed oct. 8, 195s s sheets-sheet s:

United States Patent l ROTARY DRIER Bryce M. Hess, Chicago, Ill.

Application October 8, 1953, Serial No. 384,871

13 Claims. (Cl. 34-1l9) This invention relates to rotary driers of the type in which a foraminous air tube is surrounded by a foraminous drum, and in particular it relates to such a drier in which the construction of the air tube, drum and ow directing baffles is such that there is constant movement of granular material from the inside of the annular drying chamber which is closest to the air tube toward the outside of the chamber, and material from nearer the outside of the chamber Works its way toward the air tube, as the drum rotates. i

Driers of this general character are quite well known,

and include a frame upon which a foraminous drum is horizontally mounted for rotation about its axis. At the center of the drum is a foraminous air tube which may be stationary or may rotate with the drum. A furnace and blower are connected to an open end of the air tube so that when the drying chamber which surrounds the air tube is lilled with granular material hot air and combustion gases from the furnace may be blown into the air tube and passed through the foraminous wall of the tube so as to diffuse through the granular material in the drying chamber. Several radial baies are secured to the drum and extend toward the air tube so that as the drum is rotated the material in the drying chamber is caused to tumble.

The drier of this invention is particularly constructed for drying green coffee, which at the present time is principally dried by spreadinga days harvest on the lioor of a patio where it is dried in the sun. The drying procedure takes about a week, and the colee in a patio must be moved under cover every night and moved out again in the morning. Rotary drum driers which have heretofore been used in the drying of green coffee have not performed the drying operation in a manner which is satisfactory for the production of coffee of the highest grade, and as a result such driers have found but little acceptance in the major coffee growing areas.`

A typical rotary drum drier which has been employed in coffee drying has a 70 inch drum with a 16 inch air tube, so that the width of the drying chamber is 27 inches. Three battles which are about 20 inches in length extend inwardly from the drum Wall, so that they project across about three-fourths of the width of the drying chamber'. In the particular drier the drum rotates independently of the air tube, and a screw vane on the outside of the air tube tends to move material from one end of the drum toward the other as the drum rotates. Such a drier is normally operated by being filled only about twothirds of the way to the top, and the batle construction combined with the small size of the air tube compared to the size of the drum produces an action within the drum in which material cascades over one side of the air tube in a rather thin layer. Since the layer of material covering the air tube in that area is so thin, substantially all of the drying air passes through that thin layer where resistance is the lowest. Thus, drying is accomplished almost entirely by bringing various incre- 2,780,010 Patented Feb. 5, 1957 ICC( ments of the total charge of granular material successively and repeatedly through that portion of the drum where they cascade over the air tube. The drier is necessarily quite slow in operation and relatively ineicient.

If such a drier is lled so that the level of material is substantially above the roots of two adjacent battles when the midpoint between the baffles is at the top of the drum, the cascading action can not take place, but instead the materialnext to the air tube tends to remain there and the material between the inner ends of the baffles and the drum wall tends to pack against the battles and not move toward the center. Very little interchange of material between the inside and the outside occurs. lf such a drier is filled even fuller, for example, -85% of the way to the top, the screw action can feed material adjacent the air tube into a packed mass at one end of the drying chamber so as possibly to fracture some of the material.

In accordance with the presentA invention a 70 inch drum has a 30 inch air tube so that the drying chamber surrounding the air tube is only about `20 inches Wide. Each of the three batllesis about 14 inches long so `that it extends about seven-tenths of the distance from the drum wall to the air tube. in spite of the fact that the baies in applicants device extend across almost the identical proportion of the Width of the drying chamber as in the prior art device above discussed, because of the larger air tube the relationship between the air tube and the battles is quite diterent in the present construction. With the l6'inch air tube of the prior art device only about 5% of an inch of the air tube projects beyond a chord drawn through the ends of two adjacent batiles. With the 3() inch air tube of applicants device about 5 1A inches of the air tube projects beyond a chord drawn between the ends oftwo adjacent baffles. Expressing this in a diiterent way, that portion of a 16 inch air tube which extends beyond such a chord subtends an arc of about 50 while that portion of a 30 inch'air tube which extends beyond the chord subtends an arc of about It is obvious, therefore, that the 30 inch air tube approaches very close to a chord between the roots of two adjacent baiiles while the 16 inch air tube barely projects beyond the chord drawn between the tips of adjacent baflles. The result of this difference in relationship between the air tube and the batlles completely changes the ilow of material in the drying drum as the drum is rotated.

Applicants drier is ordinarily filled nearly nine-tenths of the way to the top, and should be lilled at least threequarters of the way to the top even after the shrinkage which takes place during drying. When iilled threequarters of the way to the top there is not much material covering the air tube, but the material is about level with a chord connecting the roots of two adjacent bales when the drum is positioned with the midpoint between the bales at the top. When the drum is filled three-quarters or more of the way to the top it produces an interchange of material between the interior of the chamber close to the air tube and the external portion of the chamber` close` to the drum wall. Insofar as applicant is awarethis is a completely unique action in a rotary drum drier, and results in a greatly increased efticiency of the drying operation. Thisis because in any such drier the drying of any particular granule of material is caused only by its contact with hot gases diffusing outwardly from the air tube, so that much more eicient drying takes place close to the air tube than adjacentthe periphery of the drum. Thus, the constant shulling of material from the inside to the outside,I and movement of material from nearthe outside of the chamber toward the air tube, results in a very efficient drying operation.

The thinnest layer `of vmaterial is where the material slides under a baille, and even there it completely lls the space between the tube and the inner end of the baille; so that the hot gases tend to diffuse out more or less uniformly over the circumference of the drum. Even toward the end of Ya drying operation, when the coffee has shrunk so as to fill only three-quarters of the drum, the interchange takes place because of the height of the bailles. They extend well into the coffee, which is about the height of chord C1 at the end of a drying operation.

The drier of the present invention is of the free air type in which a large volume of air is blown through the drying chamber at relatively low temperature so that the moisture is carried away as rapidly as it'vaporizes from the material. -For example, in the present drier the air enters the air tube at 180, and the volume and rate of air ilow are at a high enough level that'the material being dried reaches a maximum temperature which is probably in the vicinity of 120. This type of drying causes no change in the structure of any vegetable material until the moisture removal is sufficiently complete that the drier begins to remove water of crystallization from the material. When this ilrst commences there is a sharp increase in the temperature of the material which makes it easy to regulate the time of free air drying so as to avoid any change in the material being dried.

The movement of material `from the inside of the drum, adjacent the air tube, to the periphery of the drum is accomplished by permitting granules adjacent the air tube to move beneath a baille and slide over the top surface of the material beyond the baille so as to pass to the periphery of the drum, and at the same time permitting material from the periphery of the drum behind the baille to slide forward and down and follow into the space near the air tube as the material slides under the baille. The precise angle at which this occurs depends upon the angle lof repose of the material being dried; and this decreases as the material dries.

Another factor which affects the efficiency of drying is the distribution of the air stream from end to end of the air tube. Since the air tube has a foraminous side wall, a closed end, and an open end through which hot air is blown into the tube, it is apparent that most of the air will ordinarily blow through the tube to the closed end before passing through the foraminous side wall of the air tube and diifusing through the granular material. In the apparatus of the present invention there is a perforated transverse baille mounted approximately midway in the air tube which changes velocity pressure to static pressure. Thus, some of the air strikes the baille and is deflected through the wall of the air tube ahead of the baille, while the balance of the air passes through the openings in the perforated baille so as to pass through the foraminous side Wall of the tube in the second half of the drying chamber. This also aids efficient use of the air stream in the drier by causing air to pass out of the air tube under substantial pressure more or less uniformly along the length of the tube, rather than piling up against the end wall and passing predominately through the portion of the drum closest to said solid end ofthe tube.

Although the`drier of the present invention is especially designed for drying green coffee, it is obviously applicable to the`drying of other materials such as corn and other grains.

The invention is illustrated in a preferred embodiment in the accompanying drawings in which:

Fig. l is a side elevational view of a rotary drier conso-called structed in accordance with the present invention;

Fig. 2 is van end elevational view thereof viewing Fig. l from the right;

Fig. '3 'is an enlarged fragmentary sectional view taken 'asfndicated along the line 3 3 of Fig. 1;

Fig. 4 is an enlarged fragmentary sectional view taken as indicated along the line 4 4 of Fig. 2; and

Fig. 5 is a fragmentary view showing a preferred construction for the foraminous air tube and drum walls.

Referring to the drawings in greater detail, and referring ilrst to Figs. 1, 2 and 4, the drier of the present invention includes an upright frame indicated generally at 10 which has front legs 11, rear legs 12, bottom longitudinal frame members 13, top longitudinal frame members 14, top transverse frame members 15, a front transverse drum support rail 16, a rear transverse drum support rail 17, and transverse base rails 18 for lateral diagonal leg braces 19 at the front and rear of the frame. The frame is about 12 feet high in the particular embodiment of the invention here shown.

Mounted on the front support rail 16 is a pair of U- shaped brackets 2i) in which are mounted support rollers 21, and mounted on the rear support rail 17 is a pillow block 22. A drying drum, indicated generally at 23, has a foraminous side wall 24, the openings24a in which are rectangular, and arranged in rows circumferentially and longitudinally (see Fig. 5), a solid annular front plate 2S having a peripheral flange 26 which is Welded to the foraminous side wall 24, and a circular rear plate 27 having a peripheral flange 28 which is welded to the foraminous side wall 24. Surrounding the inner margin of the annular front plate 25 is an outwardly projecting angle member 29, and substantially aligned with the angle member 29 on the inner face of the rear plate 27 of the drum is an annular angle member 363; While supported between the angle member 29 and the angle member 30 is a foraminous air tube 31 which is concentrically positioned in the drum 23. Secured to the rear plate 27 of the drum is a plate 32 on which is a boss 33 for a ystub shaft 34 which is supported in a bearing 35 in the pillow block 22, and at the front of the drum 23 the projecting flange 29 rests upon the rollers 21. Thus, the drum and air tube form a unit which is rotatable about its horizontal axis.

As best seen in Fig.v3, the drum 23 is provided with `three radially extending bailles 36 which are evenly spaced about the drum and extend inwardly approximately seven-tenths of the distance from the side wall 24 of the drum tothe air tube 31. In the illustrated embodiment of the invention the drumA 24 is 70 inches in diam eter and the air tube 31 is 3() kinches in 4diameter so that the drying chamber 57 which is formed in the space between the side Wall 24 and the air tube 31 is 20 inches across, and the baflles are 14 inches long. The proportions of the drum 24, air tube 31 and bailles 36 are such that a chord C1, indicated by a dot-dash line, drawn between the roots of two adjacent bailles 36 is about seveneighths of the distance from the drum 24 to the air tube 31, while a chord C2, indicated by a triple dot-dash line in Fig. 3, is about one-third of the way from the wall of the air tube to the center. rhus, about 51/2 inches of the air tube projects beyond the chord C2, and as shown by the radii R1 drawn to the points at which theichord C2 cuts the air tube,`the arc subtended by the vchord is somewhat greater than It isapparent from the foregoing dimensional factors that yas the drum 23 rotates the tip of a baille 36 moves past a vertical line tangent to the air tube 31 oniy after the baille-has moved aconsiderable distance beyond a vertical radius; and in the illustrated embodiment the baille occupies a position approximately 50 from the vertical before this takes place. ln the prior art evice heretofore referredfto, a baille is at an angle of about y30" from the vertical Whenits inner end passes a vertical line tangent to the air tube.

To obtain the desired movementof material within the drying chamber 37 as'the drum is rotated it is necessary that the drum be filled quite full. In order topermit the drier to .be used either on a load of*V given .size or a load of about half the given size, and st ill inveach case fill the drum to the desired level, as best seen `infFig.l 4,

the drying chamber.

5 an annular' partition 38 divides the drying chamber 37 into two qual size compartments 37a and 37b. In conjunction with the partition 33 there is a rotatable shaft 39 which extends through a fitting 40 in the foraminous wall 24 of the drum and through a fitting 41 in the foraminous wall of the air tube 31 and has its inner `end journaled in a second fitting 42 in the wall of the air tube. A handle outside the drum permits the shaft 39 to be rotated manually. Mounted on the shaft 39 within the air tube is a circular partition 44, which in one position of the shaft 39 lies in the same plane as the partition 38 so that the movement of air in the air tube is confined to that portion lying within the compartment 37a of the drying chamber. Thus, if a full load is to be dried the two compartments of the drying chamber are filled to the desired level and the drying operation is carried out with the circular partition 44 in the air tube occupying the position shown in Fig. 4 in which it is perpendicular to the plane of the partition 38; while if a half load is to be dried the circular partition 44 is rotated 90 to position it in the plane of the partition 38 and only the compartment 37a of the drying chamber is used.

As best seen in Fig. 3, a perforated baflie 45 is mounted on the shaft 39 perpendicular to the partition 44 so that when the entire drying chamber 37 is being employed in the drying of material the perforated baffie extends across the air tube in the plane of the annular partition 38. The perforated bafiie 45 assists in providing fairly uniform distribution of the air stream from end to end of the air tube 3i, because air which impinges against the solid parts of the perforated baffle 4S is deected into the compartment 37a of the drying chamber while air which passes through the opening 45a in the perforated baffle is deflected by the end wall 30 of the air tube into the compartment 37b. Thus, velocity pressure within the air tube tends to be more uniform than is possible without such a perforated baffle.

Mounted on the top longitudinal frame members 14 is a garner 46 through which granular materia-l may be introduced into the drying chamber 37 through a pair of longitudinally spaced apertures 47 and 48 which are formed in the wall 24 of the drum 23 so as to admit material to the compartments 37a and 37b, respectively, of A transverse inverted V-shaped partition 49 divides the lower end of the garner into feed openings 50 and 51 which are aligned, respectively, with the openings 47 and 48 in the wall of the drum. As best seen in Figs. 3 and 4, there are circumferential flanges 52 and 53 which ank, respectively, the openings 47 and 48 to serve as guideways for circumferentially slidably closure members 54 and 55. As seen in Fig. 3 the center lines of the openings 47 and 48 coincide with a radius through one of the baffles 36, so that when the drum is positioned with the openings at the top where material may be received from the garner 46 the streams o-f material entering the openings are split by the baie 36 and iiow more or less uniformly into the two sides of the drying chamber 37. The positioning of the openings 47 and 48 with respect to the baffle 36 assures that the entire lower part of the drum, beneath the other two baffles, will fill with material. What is even more important it assures that when the drum is in dumping position as seen in Fig. 3, all the material will slide off the two bafiies 36 which are uppermost, and no dried material will be trapped in the drum above the baffles.

Fastened to the bottom longitudinal frame members 13 in line with the openings 47 and 48 in the drum wall is a pair of discharge hoppers 56 and 57 to receive discharging material from the openings 47 and 48, respectively. Control of material flow through the discharge hoppers S6 and 57 may be effected by gates 58 and 59 which are slidably mounted in flanges 66 and 61 in the throats 62 and 63 of the discharge hoppers 56 and 57, respectively.

Hot gases for drying material in the drum 23 are provided by a centrifugal blower 64 which is driven by a motor 65 through a belt drive 66. The blower 64 takes hot combustion gases from a furnace 67 and delivers them through a hot gas conduit 68 to the air tube 31 of the drier drum 23, the innerend of the hot gas conduit being restricted as indicated at 69 to extend into the end of the air tube 31 to provide a gas tight connection between the stationary tube 68 and the rotatable tube 31.

A drive motor platform 70 is mounted between the rear legs 12 of the upright frame 10, and is provided with diagonal braces 71 and 72 which bear against said legs. As best seen in Fig. 2, a motor base 73 is secured to the platform 7 0 by means of a hinge 74 so that the base 73 may tilt about the hinge; and mounted on the base 73 is a drum drive motor 7S, the shaft 76 of which makes a direct connection with a gear reduction unit 77, which is provided with an outputshaft 78 having a pulley 79. A flexible V-belt surrounds the end of the drier drum 23, as best seen in Fig. 1, and is driven by the pulley 79 so that operation of the drum drive motor 75 will rotate the drum 23. The hinged mounting of the motor base 73 permits the weight of the motor and gear reduction unit to be carried partly by the belt 80, so as to tension the belt, and automatically compensates for belt wear. The gear reduction unit 77 combined with the relative dimensions of the pulley 79 and the drum 23 provide a speed reduction such that the drum is rotated at about 1%. revolutions per minute.

The use of the unit is believed to be clear from the foregoing description. The drum 23 is rotated to a position such that the openings 47 and 48 are at the top, immediately beneath the garner 46, and the slidable closures 54 and 55 are opened. The drying chamber 37 is filled with material, land the closures 54 and 55 are closed. The drumiof a commercial unit may conveniently be six feet in diameter and six feet long, and with an air tube of 30 inches diameter the total volumetric capacity of the drying chamber 37 is suiiicient to accommodate 6200 pounds of wet coffee. The drier is filled about halfway up the blaflie which is adjacent the openings in the drum at which level the drum is filled about nine-tenths of the way to the top and contains about 6000 pounds of coffee.

The heating unit and associated blower are put into operation, as is the motor for rotating the drum; and drying is carried out by blowing heated air through the air tube so that it mfay diffuse outwardly through the drying chamber as the drum rotates Rotation of the drum produces a constant shuffling of material from the portion of the drum adjacent the air tube to the outside, and a forward and downward following movement of material from behind the biaie toward the air tube, so that all material in the drum is subjected periodically to the hottest, driest air diffusing outwardly from the air tube. The drying operation may be controlled in the usual ways known to the art to reduce the moisture content to the desired level. When drying has proceeded to the desired extent the machinery is stopped with the doors in the drum Wall in register with the outlet hoppers, so that the contents of the drier may be dis-charged for further processing.

The foregoing detailed description is given for clearness of understanding only and no unnecessary limitations are to be understood therefrom, as some modifications will be obvious to those skilled in the art.

I claim:

1. A rotary drier comprising: a horizontally disposed cylindrical drum having a foraminous side Wall, one solid circular end plate and one solid annular end plate; a foraminous air tube extending through said drum with one end supported on said annular end plate and the other on said circular end plate so that the air tube has `an open end and a closed end, the space between the side wall and the air tube forming a drying chamber; a plurality of longitudinal, radially extending baiiies secured to the drum with their inner ends spaced from the air tube; asolid transverse partition dividing the drying chvamber into two parts; movable baille means in the air tube including a perforate baille and a solid baille, said batlles being movable to position either one transversely of the air tube in line with said transverse partition; means for blowing hot gases into the open end of said air tube; and means for rotating said drum.

2. The drier of claim 1 in which a rotatable rod extends across the diameter of the drum and has a handle outside the drum, and the perforate and solid bailles are both mounted on said rod in perpendicular relationship to one another.

3. A drier comprising: a frame; a drum supported in said frame for rotation on a horizontal axis, said drum having a foraminous side wall, an annular end plate and a circular end plate; a concentric, central air tube extending from end to end of said drum to deiine the inner wall of an annular drying chamber, said lair tube having a toraminous side wall and being supported on said end plates so as to have an open end and a closed end; three evenly spaced radial brallles mounted in said drum with their inner 4ends spaced from 4the airtube; material intake and outlet door means in the wall of said drum, the center line of said door means being common with the line of one of said bailles; a material garner labove the drum by means of which granular material may be fed into said door means in one position of the drum; a discharge hopper below the drum through which material may be dumped from the door means in 'another position of the drum; means for blowing hot air into the open end of the air tube, and means for rotating the drum and air tube as a unit.

4. `The drier of claim 3 in which the drum has a solid annular partition surrounding the air tube midway`of its length to divide the drying chamber into two plarts, and the door means has a portion on each side of said partition.

5. The drier of claim 4 in which there is a movable solid battle in the air tube which vmay be positioned transversely of the air tube in line with the annular partition in the drying chamber.

6. The drier of claim 5 in which the solid baille in the air tube is mounted on a transverse lrod which has a portion outside the drum, and a perforate baille is mounted on said rod perpendicular to said solid battle so that either of said baflles may extend across the air tube and their position may be manually controlled by means of said rod.

7. A rotary drier for drying a mass of granular material comprising: a horizontally disposed foraminous air tube having an unobstructed outer surface; a foraminous drum surrounding said air tube to form an annular drying chamber dened by said air tube and said drum; wall means which dene the ends of said chamber; a plurality of longitudinal inwardly extending radial bailles secured to the drum at their roots and having their inner ends spaced from the air tube, said drum and battles and air tube being so proportioned and the number of battles being such that the air tube is more than halfway from the l center of the drum to a chord extending betweenV the roots of two adjacent bales, while said chord passes outside the air tube; means for blowing hot gases into said air tube; and means for rotating said drum.

8. A rotary drier for drying a mass of granular material comprising: a horizontally disposed toraminous air tube having an unobstructed outer surface; a foraminous drum surrounding said air tube to form an annular drying chamber dened by said air tube and said drum, the radius of the drum being about twice the radius of the air tube; wall means which define the ends of said chamber; three longitudinal `inwardly vextending radial bailles secured to the drum at their roots and having their inner ends spaced from the air tube, the circumference of the air tube bearing such a relationship to the inner ends of the baflles that a chord through the inner ends of two adjacent balles passes through the air tube; means for blowing hot gases into said air tube; and means for rotating said drum.

` 9. A rotary drier for a mass of granular material, comprising: a horizontally disposed foraminous drum having a orarninous axial air tube therein and end walls dening with said drum and air tube a drying chamber which is annular in cross section; means for blowing hot into the air tube; means for rotating the drum; and a plurality of longitudinal, equally spaced, radial bafiles which have their roots secured to the drum and their inner ends spaced from the air tube7 relative dimensions ot said air tube, said drum and said baffles being such that the radius of the drum is about twice that of the air tube and tl e battles extend about of the distance from the drum to the air tube, and the number of battles being such that a chord drawn between the inner ends of two adjacent bathes passes through the air tube oil the center thereof.

l0. A rotary drier for a mass of granular material, comprising: a horizontally disposed foraminous drum having a toraminous axial air tube therein and end walls dening with said drum and air tube a drying chamber which is annular in cross section; means for blowing hot gases into the air tube; means for rotating the drum; and a plurality of longitudinal, equally spaced, radial batlles which have their roots secured to the drum and their inner ends spaced from the air tube, the radius of said drum being about twice that of said air tube, and the radial dimension, andl number of said ballles being such that a chord extending between the roots of two adjacent bafiles passes outside the air tube while a chord between the inner ends of two adjacent ballles passes through the air tube.

11. The drier of claim 10 in which the air tube is more than halfway from the axis of the drum to the chord extending between the roots of two adjacent bafiles.

12. A rotary drier for a mass of granular material, comprising: a horizontally disposed cylindrical drum having a foraminous side wall, one solid circular end plate and one solid annular end plate; a foraminous air tube extending through said drum with one end supported on said annular end plate and the other on said circular endplate so that the air tube has an open end and a closed end, the space between the side wall and the air tube forming a drying chamber; means for blowing hot gases into the open end of the air tube; means for rotating the drum; and a plurality of longitudinal, equally spaced, radial battles which have their roots `secured to the drum and their inner ends spaced from the air tube, the relative dimensions of said air tube, said drum and said bailles being such that the radius of the drum is about twice that of the air tube and the baffles extend about 70% of the distance trom the drum to the air tube, and the number of balles being such that a chord drawn between the inner ends of two adjacent bales passes through the air tube off the center thereof.

13. The drier of claim 12 in which a foraminous baf- 'tle extends across the air tube about midway of the length of the air tube to partially convert velocity pressure of gas to static'pressure.

References Cited in the ille of this patent UNITED STATES PATENTS 535,560 Schmiedecke et al Mar. 12, 1895 544,570 Echeandia Aug. 13, 1895 549,473 Zeckendorf Nov. 5, 1895 625,651 Declerco May 23, 1899 850,398 Ramos Apr. 16, 1907 1,521,773 lohnson Jan. 6, 1925 

